1. Field of the Invention
This invention relates to an ignition for an internal combustion engine wherein the ignition timing of an internal combustion engine is electronically computed and selectively adjusted as a function of engine knock.
2. Prior Art
Ignition timing of an internal combustion engine is varied in accordance with the operating conditions of the engine so that optimum operation of the engine is insured. It is generally known in the art that for increased efficiency and reduced fuel consumption of an engine the engine should be ignited with the minimum spark advance for best torque (MBT). Ignition timing of the engine must be varied in accordance with the engine operating conditions to ignite the engine at the MBT. It is also known that MBT is related to cylinder pressure as a function of crankshaft position angle. That is, when maximum cylinder pressure occurs at a certain desired crankshaft position angle, the cylinder is operating at MBT. The particular crankshaft position angle depends upon engine design parameters and occurs at a smaller spark angle advance than that where knocking begins.
Known ignition timing control systems establish the ignition timing of an engine by detecting the engine speed by a centrifugal advance mechanism and by detecting the intake vacuum pressure by a vacuum advance mechanism to represent the operating conditions of the engine. In recent years, there has been increased use of electronic circuitry in the operation of and control of internal combustion engines. For example, an electronic engine control can adjust the spark timing of an engine.
A disadvantage of the prior art systems is that since an ignition timing has been programmed on the basis of the test results of an internal combustion engine, there are instances where the ignition timing considerably deviates from the actual MBT. That is, the programmed ignition position differs from the actual ignition point due to the atmospheric conditions, variations in characteristics among engine of the same type, etc. Further, the adjustment of the spark timing is applied equally to all cylinders. Such an adjustment does not necessarily produce ignition of each cylinder at the MBT. Just as characteristics and operating conditions of entire engines vary, characteristics and operating conditions of individual cylinders in engines vary. These are some of the problems this invention overcomes.